Energy company E.ON Sweden is using a novel district heating system that leverages heat from a waste incinerator plant boosted by four GEA ammonia (R717)-based heat pumps to supply heating for 10,000 homes In Malmö, Sweden.
Not only that, the heat pumps are tapping heat from a local wastewater treatment plant. Vahterus heat exchangers are employed to facilitate the heat recovery process.
Installed in May 2021, this system saves around 50,000 metric tons of CO2e per year, said GEA. This helps E.ON achieve a climate target, set in 2017, to provide 100% recycled or renewable energy to its customers by 2025.
Using GEA Grasso Screw compressors, the four heat pumps operate in parallel to provide 40MW (11,374TR) of total heating capacity with outflow temperatures around 66°C (151°F).
“Each [heat pump] has a coefficient of performance (COP) above 3.5, so for each 1kWh of electricity used by the heat pump, 3.5 kWh of heat is produced for the city,” said Kenneth Hoffmann, Product Manager of Heat Pumps at GEA.
From October to April, the pumps operate at 100%, and during peak summer use, only one or two heat pumps are required. The system provides 8% of Malmö’s heating demand, delivering 200GWh a year, Vahterus said.
Utilizing clean wastewater
The system draws nearly 30MW (8,530TR) of heat from treated sewage water that has a constant temperature of 14°C (57°F), cooling it to 8°C (46°F) before releasing it to the sea, said Vahterus. Using the clean wastewater increases the system efficiency by 15% over using seawater for the heat pumps and 10% over groundwater, the company added.
“Since there can be some organic material in the wastewater, the Shell & Tube evaporators have been fitted with a ball cleaning system that continuously cleans the stainless-steel tubes to avoid fouling in the heat exchanger and maintain high efficiency without having to stop the heat pump,” the company said.
Separately, recirculated city water returns to the waste incinerator at temperatures close to 50°C (122°F) and is heated by the flue gas economizer to 55°C (131°F) before entering to the heat pump, said Vahterus. Supported by the heat exchange with the wastewater, the heat pumps raise the city water temperature to 66°C (151°F) and return it to the waste incinerator plant where it is heated to the temperature required by the district network, which varies from 70 to 90°C (158 to 194°F).
“The heat pump is designed to deliver up to 80°C [176°F] but will rarely be required to deliver temperatures above 71°C [160°F],” GEA said.
Ammonia was selected as the refrigerant for its ability to meet EU f-gas regulations with zero impact on global warming, easy availability and low cost.
“It would have been cheaper to install an R134a heat pump, but we didn’t believe in that refrigerant for the future,” said Mats Egard, Project Manager at E.ON Värme Sverige AB. Vahterus estimates that using ammonia may save 80% of the refrigerant cost over available HFO alternatives over the system’s expected 20-to-30-year lifespan.
E.ON did not immediately respond to a request for comment on the current status of the district heating plant.
Headquartered in Düsseldorf, Germany, GEA Heating and Refrigeration Technologies provides industrial and commercial heating and cooling solutions.
Vahterus is a family-owned business in Kalanti, Finland, providing welded plate and shell heat exchangers.
“Each [heat pump] has a coefficient of performance (COP) above 3.5, so for each 1kWh of electricity used by the heat pump, 3.5 kWh of heat is produced for the city.”
Kenneth Hoffmann, Product Manager of Heat Pumps at GEA
